Modern Mythology: Flushing Toilets & The Coriolis Effect

Have you ever seen that episode of The Simpsons where the Simpsons go to Australia? In it (the usually quite on to it) Lisa explains to Bart that the toilets in the southern hemisphere flush in the opposite direction, due to the Coriolis effect. A very skeptical Bart then racks up a massive phone bill trying to establish if this is true or not (and then gets indicted for fraud, hence the visit to Australia).

Well, Bart was right to be skeptical of this claim. It isn’t true, although the effect that supposedly causes it is real. The confusion about this myth comes from applying a real, observable, scientific principle to a situation where it doesn’t fit. The Coriolis effect describes the deflection of objects in a moving reference frame, such as large weather systems (i.e. hurricanes) on the earth, and ballistics. However, the water in a flushing toilet is too small to be influenced by the rate of rotation of the earth.

There are some pretty hilarious videos on YouTube about this, where people flush toilets in both the northern & southern hemispheres, and get lucky that they happen to flow in opposite directions. Thus, by their comprehensive study involving lots of toilets in both hemispheres (NOT) they “demonstrate” that the trope is true. However, no consistent differences have been observed between toilets in the northern & southern hemispheres.

Or, this one, where some tourists witness a guy doing a demonstration on either side of, and on, the equator:

Notice how he can flick his wrist slightly to influence the direction? And how it starts spinning slightly (although not much) on the equator and he lifts the bowl up and then the camera turns away pretty quickly thereafter. Yeeeeaaaaa….

In any case, water in toilets flushes in the direction the bowl is designed to flush in, or in the case of drains, the shape of the sink and how level it is.

Here are some vids explaining more about the Coriolis effect. The second one is especially cute.

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